Active faulting of the southeastern-most Zagros (Iran): Microearthquake seismicity and crustal structure

Abstract

The microseismicity of the southeastern-most Zagros is examined by high-resolution data recorded by a temporary dense local seismic network. The seismicity defines a diffuse pattern, mostly located beneath folds in the southern part of the High Zagros Fault (HZF). Seismicity dips gently northward in the depth range 6–25km, implying slip on a major intracrustal thrust fault extending to the north of the Main Zagros Reverse Fault (MZRF) which seems to connect to the Mountain Frontal Fault (MFF). Furthermore, observed focal mechanisms suggest transpressive motion on the HZF located west of the Zendan-Minab-Palami (ZMP) fault system and striking obliquely to the convergent motion. These observations suggest that the transition zone between the Zagros continental collision zone and the Makran oceanic subduction zone is not confined to the east of the ZMP and some part of the this diffuse transition is accommodated north of the Hormuz Strait in the west by partitioning between strike-slip and shortening components. The Zagros reverse domain is terminated by a transpressive tectonic regime. Moho depth beneath the MZRF, deduced from receiver functions, is almost 45km thinner than is observed in the central and northern parts of the Zagros. These observations support a model of active underthrusting of the Arabian plate beneath central Iran in the southeastern-most Zagros.